


Coming of Age

by Andromeda_Schwarz



Category: Undertale (Video Game)
Genre: Dom Sans, Ecto-Penis (Undertale), F/M, Implied Pregnancy, Implied/Creampie Kink, Light Dom/sub, Reader Is Not Frisk, Slight Corporeal Punishment, Slight/Non-Con, reader is female
Language: English
Status: Completed
Published: 2016-07-04
Updated: 2016-07-04
Packaged: 2018-07-20 00:50:53
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,511
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7384432
Author URL: https://archiveofourown.org/users/Andromeda_Schwarz/pseuds/Andromeda_Schwarz
Summary: <blockquote class="userstuff">
              <p>It's finally the day where you hit the big One-Eight. You reflect on your time underground spent with everyone, and you linger on the thoughts of the Skelebros who you stayed with and slowly after you grew older you found yourself attracted to their little  intricacies. </p><p>Little did you know, the eldest had known about this the day it started, and he has a present to suit the desires you had refused to allow see the light.</p>
            </blockquote>





	Coming of Age

**Author's Note:**

> Whelp, this is my first story here on AO3! This is something I typed up in my free time, I was writing a more full length story but I feel like it's rushed so I'm going back to re-edit it to flesh it out a bit more. Though I don't know when I'll get to that exactly... Heh-heh...
> 
> Anyways enjoy this newbie story! I haven't written anything in YEARS

Today was the day, she was coming of age, it was her 18th birthday, and marked 10 years of her living underground. She had fallen down here when she was 8 years old and after much struggle and strife due to injuries and a few bad encounters, she had been taken in by the Skelebros. Two eccentric monsters who resided in Snowdin, they were pretty much the life of the town it seemed like with their brotherly antics. It was quite a sight to see and never ceased to amuse you with the playful banters these two would have. 

 

Sans and Papyrus was their names, Sans being the older one, but shorter, he was a laid back super chill guy who loved to tease his younger brother. Despite of how lazy he seemed he actually managed to get quite a lot of things done behind his brother’s back, keeping that illusion that he was lazy. It left her feeling confused to this day as to why he did that, maybe to make his younger brother Papyrus feel so much more important. Sans worked several jobs it would seem like always seeming to be busy, bouncing around but somehow managing to look lazy the entire time, he also was a scientist…such a lazy guy you wouldn’t expect to be a super genius, the guy was incredibly intelligent and even more so observant, he barely needed to glance at you to tell if something was wrong, it’s like he could sense the aura that something was up. That always troubled her a bit. He could detect any slightest change in anyone the second it happened and was able to determine what it was before the person themselves seemed to noticed what it was. 

 

That kind of intelligence…was…attractive. 

 

She didn’t know when it happened, hell maybe during her pre-teens when her hormones began kicking in and such, but she started noticing things about the older brother that she never picked up as a younger girl. His laid back lazy nature, and his chill grins and smirks, instead of infuriating and being his trademarks, was turning into quite attractive features of his overall being. The way he looked at you when you came in late one day, you had snuck out to go relax in the clearing of Snowdin to enjoy the snow, even after both Papyrus and Sans had advised her not to. He was relaxing on the couch with his legs propped up on the coffee table and arms on the back of the couch, eyes closed, she assumed he was asleep so she planned on just walking up the stairs, though soon as she closed the door, his deep baritone voice flowed to her ears. 

 

“you know you’re in trouble right? You snuck out when I had told you not to, thought you were gonna get away with it? Sorry to tell ya but I’m not stupid.” That smirk he gave her and the look in his eyes that were furious but also somehow oh so attractive to her messed with her insides so much. 

 

He still punished her and gave her and spanking to top it off. He was mad at her and did corporeal punishments when she had done something especially bad but at this age, because of her attraction to him, it only served to slightly arouse her. 

 

How had she grown to be so fucked up after being raised in a supposed pure environment? Maybe that was the problem all together. 

 

It may have seemed shocking that a human would be attracted to the symbol of death, skeletons, but these guys, everyone in the underground was different, they weren’t exactly skeletons in the regard we see them as. With Sans and how his eye sockets are just dark voids with white pinpricks that trained in on you, those were his eyes. Normal human skull eyes didn’t have that empty space you could see the white back, speaking of human skulls, his, in overall shape was not normal compared to humans. Papyrus was more similar in that regard. But even how Sans was able to close his eyes and how his face was so expressive, his bone was malleable, and so was his brother’s. Their bodies were their souls, and infused entirely of magic, the skeletal appearance was only the form it decided to take. 

 

Speaking of magic, these two were especially powerful. Papyrus was really powerful in brute strength and he was incredibly agile, super speedy and would seem to dance around the battle field in training. It constantly brought questions to her mind how he wasn’t in the Royal Guard, he was constantly training to be in the Royal Guard and Undyne, the captain hadn’t let him in, but constantly trained with him. You had found out from Sans that the reason Undyne didn’t let him in was due to the fact that Papyrus didn’t have the heart to hurt anyone, despite if they even hurt him. Although during training, because it was training he let all his skill show. 

 

It was really hot. 

 

His usually demeanor of being so innocent and sweet seemed to vanished and his eyes would turn cold and his face serious and he would dash around the battlefield like a lightning bolt and sparring with Undyne, she would have a great amount of trouble fairing off against Papyrus, he was so fast and strong simultaneously that it was almost overwhelming, he even managed to beat her a few times. But once the sparring was over he would be back to his usual self. It was almost as if he had two different personalities. The one he displayed during training was that of like a commander and a super soldier, and lord did that rile you up. It didn’t help that Sans took noticed the way her gaze was changing from amazement to slightly heated over when she was watching him one day. 

 

He teased her about it relentlessly. 

 

Sans on the other hand, he rarely let his power show, he seemed like he was some important defender and he was a last resort method, the look in his eyes sometimes reminded her of those hardened soldiers she saw on the surface when you still lived up there. You had caught him fighting against something one day out in the forest. She couldn’t catch what it was because of the multiple blast of magic coming from Sans. 

 

Sans was fast...really fast…and super evasive in terms of dodging. And just overall really strong. 

 

She thought his hand hurt when he spanked her on the rare occasions but seeing how he slammed the opponent he was fighting around like a rag doll with so much force. How rocked the ground with bones and how he easily dodged attacks like they were nothing, like wasn’t breaking a sweat. It made her realize just how powerful the two brothers were, and she was glad to have them on her side. 

 

The brothers were a force to be reckoned with. 

 

That aside, it was her birthday, and she had quite the gathering at the house, Undyne and Alphys, who was the Royal Scientist she had befriended and found out that both Sans and Alphys worked together time to time. She also discovered that Undyne and Alphys had gotten together. The two were adorable. There was also Grillby, he was the bartender of the restaurant in Snowdin, he served the best food, he was a fire Elemental and it confused her as to why he resided in Snowdin, he was really hot though, not as in temperature but actual appearance, his body seemed humanoid alike, with a broad buff chest and toned biceps and shoulders, his suit fitting him snug, and his glasses somehow staying on his face added to that. 

 

The KING of Monsters decided to show up to her party too, he was a very large monster, a boss monster she come to learn. He was incredibly broad and muscular but was super friendly. His sharp horns always worried her though. He was a goat monster after all, and apparently his Ex-wife, Toriel, though it seemed like they were getting back together slowly, showed up as well, she’s a beautiful motherly goat monster that always warmed your heart, she always had an aura of comfort surrounding her. You adored her. 

 

She didn’t allow Mettaton, the underground celebrity to come, she didn’t need that kind of attention at her party. Overall though it was a great gathering, Toriel made a massive pie and cake for her which everyone shared, it was absolutely delicious. Everyone partied and danced the day away, and you were a dancing demon, she loved music, a bunch from her world had fallen down over the years, she assumed someone was disposing of a collection. That was perfect though because the songs, she absolutely loved, she danced hard until she was a sweating mess, and continued to dance afterwards, letting the rhythms flow through her and rock her body around. She picked up on how Sans eyes would lighten in amusement at how happy and wild she was getting with her dancing. If anything that egged her on. Eventually evening then night came and people began to file out.She collapsed on the couch a sweating mess. 

 

She noticed a heavy weight drop to the side to her seeing Sans sitting there with mirth in his eyes, she rolled her eyes at his expression. 

 

“What?” She asked amused in her tone. 

 

“dancing nymph.” She let out an exhausted laugh and laid down on his lap breathing hard, he began to brush her hair through his bony fingers. 

 

“That was so much fun…thank you both for the life you’ve given me…” she said suddenly relaxing under his ministrations, his hand jolted, obviously not expecting that. Then he let out a low chuckle. 

 

“no problem kiddo, it was a fun ride.” Her brow quirked up at his wording, ‘was’? 

 

“Whaddya mean ‘was’? You planning on getting rid of me?” She let out a small laugh and so did he patting her forehead. 

 

“nah, just assumin’ you might’ve been wantin’ to be moving out now that you an adult and all.” She gave him a look that read that was screaming ‘you’re kidding me right?’ 

 

“Seriously Sans, you’re the super genius here,” he scoffed and rolled his eyes. “haven’t picked up that I’m pretty attached to you guys and no one else?” She let off a little laugh, “What, ya think I’m gonna run off with Grillby or something? I mean he’s hot and all but still.” He snorted. 

 

“ya patella a joke there, girly?” 

 

“Oh no more kiddo?” 

 

“dunno if ya gotten a look at yourself but you ain’t exactly a kid no more.” That statement caught her off guard, so much so she starts blushing mad crazy. That meant he was paying attention to your figure, and just imagining the guy eyeing you like that was enough to send pleasurable shivers rocking through your body. 

 

“your expression is leaving little to the imagination.” Instinctively you covered your face to hide your blushing madness. You felt his hands grab your wrists. 

 

“mm…no no…let me look at your adorable face. You thought I hadn’t noticed hmm? That I hadn’t taken notice of that voluptuous body you got? And that I wouldn’t notice you were attracted to me? You’re pretty bad with subtlety, been noticing your attraction to me since you were thirteen.” That made you groan, and he proceeded to laugh at you. 

 

“and tibia honest…” you felt his hand move from your head down your shoulders and how he began to grope your sides in a way that made you gasp and sent pleasurable shivers down your body. 

 

“at first it didn’t bother me, but then when you were getting closer to this age…the way your clothes fit so snug on you. Lord…it was rattling me.” You let out a nervous laugh. You weren’t expecting Sans to be…attracted to you, and how he was holding you was giving you some small insight into his domineering nature that he might have in bed, and that excited the fuck out of you. 

 

“Heh…heh…how so Sans?” 

 

“well…” you looked up at him and his grin had turned leering, he was giving you a look that promised things, things that made your stomach churn in desire. Soon before you knew it you had been slammed on the couch, you being under him. YEP! There’s that power! Boy did you get off on it! 

 

“let’s start off with your slender shoulders…lord how your smooth skin stretches beautifully across the bone, so shapely.’ His hands smooth out over the expanse of your collarbone and shoulders. “then these massive fucking tits, how did you even find a bra to fit these things in? It was fine at first but…” he grabbed your breasts almost possessively and you couldn’t help arching into him a bit. “they just kept growing and growing, to the point every movement you made they were bouncing, do you know how crazy you were driving me with your dancing you fucking tease.” Holy shit. 

 

His hands slid down to your narrow waist, it still surprised you how in shape you stayed, you would have to thank Papyrus for not letting you succumb to lethargy, because you definitely felt a lot better about your body image because of it. Your stomach was toned and your breasts had a natural lift, your butt being perky and round, voluptuous. 

 

His hands continued down to your hips. “and god damn these hips, the way you sway them, when you started growing more you starting sashaying these things around like it was nothing, mesmerizing me and everyone else with these child-bearing hips. It drove me fucking insane I wanted to breed you.” You couldn’t help the raunchy moan that left your mouth. His smirk turned absolutely devilish to this. “oh? Is that what you want? ya want me to cum in your tight little pussy and breed you hmm?” you unintentionally arched your back into him. 

 

Fuck this body. 

 

He placed his hand on your stomach and pushed you back down on the couch, “we’ll get to that soon enough” WHAT?! SANS?! 

 

“mmm…man, and this ass…” his hands moved under you and groped your ass tightly. “it’s just so fat…so round and bouncy, the way your jeans barely contain it makes me damn near lose it, and when you wear skirts or dresses, like today and you dance around like that I can’t help but wanna smack the shit out of it. Fuck you’re so sexy, how did I keep my hands off of you for so long?” 

 

All that talk alone was enough to get you wet without any prep, that talk was foreplay. Holy shit this man had a silver tongue. 

 

“now that that’s done…I can smell how fucking wet you are you little vixen. Ya want me to fuck you that badly huh? trust me I know, and since it’s your birthday, I’ll give you your present now.” He hiked your dress up and practically ripped your panties up exposing your womanhood which was absolutely soaked with your fluids, it was pretty embarrassing how aroused you had got from his words alone. 

 

“it’s like a fucking ocean down here, all this for me hmm? And I thought it was your birthday.” Soon before you knew it his head had ducked between your legs forcing your legs apart with his hands and he delved his ectoplasmic blue tongue into your folds, lapping at all the fluids like a dog. He seemed almost delirious, but that wasn’t saying much considering how much you were bucking your hips to his skull. He was driving you insane, you had the suspicion this man you had grown so attracted to would be good in bed but holy shit. 

 

His tongue curled around your clit and seemed to tug at it, then he caught you off guard by shoving two bony finger into you and curling them in a come hither motion and with one more twist your orgasm ripped through you and he lapped up all the fluids like it was his favored ketchup. 

 

“while I could eat you out all night there’s something else I wanna give ya.” With that, you watched as his blue eye flared and you saw trail of his blue magic move down his body, it enraptured you and it ended at his pelvis, the glow staying there and seeming to grow, you noticed the bulge there and you gulped at the size. It only made him smugger. 

 

He pulled down his shorts enough to expose his length, it was blue, same color as his tongue but average in length but it had a frightening about of girth. 

 

“ready for me to grant your wish birthday girl?” you nodded dumbly, you were kinda still staring at his dick, it was really beautiful despite how stupid that sounded. 

 

Him grabbing one of your thighs and hugging it to his body and kicking your other leg further out to stretch you out the most to accommodate him. He grabbed his length with one hand and slowly slipped the tip into you, the texture so slimy like honey, it felt so damn good. He brought his hand back up to wrap around the leg he had in the air and then proceeded to enter fully. God how he stretched you, despite this being your first time it didn’t hurt, probably because of how wet you were and how slimy and lubricated feeling his cock was. You were grateful for that. 

 

He then rocked his hips in and out slowly, his breathing picking up, he was watching you carefully, eating up your facial expressions. You tried to hold his gaze but it was so dominating and smug you could barely hold it; it was embarrassing but getting you off too. 

 

“look at me baby, I want you to look at me when I fuck you.” Shit 

 

Like you couldn’t control it your eyes snapped up to him and stayed focused on him as he rocked his hips in and out of you. It was doing things to your heart. 

 

Then he began to pick up, his gentle pace became hard and deep. He was smashing a spot deep inside of you that had you practically screaming, you weren’t too worried since Papyrus went to sleep over with Undyne and Alphys after the party. Wait did they plan this? 

 

His grunts as he was getting off on this too was growing in volume, it almost seemed like he was growling a bit, and that look in his eyes was becoming more glazed and animalistic. 

 

“you’re fucking mine now got it? I better not catch you running off with anyone else, I’m the only one who can see that beautiful fucking face your making right now, and hear those sounds coming out that pretty little mouth.” The grip on your leg was becoming bruising as his thrusting grew more in intensity. 

 

Your back was arching to meet him, you were delirious from him, the pleasure he was giving you and the words he said to you was making you mad. 

 

“you ready for this baby, want me to pump you full of my seed and breed you kitten? want me to mark you as mine?” He had taken over your mind, all you could think about was him. “YES! OH GOD YES SANS PLEASE! CUM INSIDE ME!” 

 

“that’s what I thought!” he thrusts became frantic and then he stilled at the deepest reach, you felt his cock throbbing in you and the second orgasm hit you like a truck and it rocked you like an earthquake, it seemed like it wouldn’t stop. His cum just kept coming in bursts, he was holding you in an iron grip and his face was scrunched up in pleasure. His moaning was strained as his orgasm racked through him. 

It was the hottest expression you seen on him. 

To the outsider it would’ve looked kind of weird to see a face like that but to you it was so fucking hot, you made him make that face, the calm and collected Sans delirious in pleasure from you. 

His deep voice even sounded a little hoarse as he groaned, his seed spilling out because there was simply no more room left. Holy shit. 

Finally, it stopped and he pulled out, his cock slopping out with a squelching sound and he admired his work. 

He patted your thigh and smirked at you, “expect to feel pretty ill tomorrow or the day after babe.” Wait what? 

 

“Sans what?!” 

 

“oh don’t give me that, you wanted it, you’re still shivering from your orgasm.” He’s not lying. 

 

“can’t wait to see our little baby bones.” 

 

Well he gave you a present alright. You placed a hand on your stomach and smiled.


End file.
